American Gastroenterological Association (AGA) recommendations on the diagnosis and treatment of OGIB: Concept and etiology OGIB refers to persistent or recurrent gastrointestinal bleeding of unknown origin, despite negative findings by gastrointestinal endoscopy (including gastroscopy and colonoscopy) and small bowel imaging. Based on the presence or absence of obvious clinical bleeding symptoms, OGIB is classified as occult and overt GI bleeding. Lesions in OGIB include those that may be overlooked by conventional gastroscopy and colonoscopy, as well as small bowel lesions that cannot be detected by imaging. Lesions that are easily missed on upper gastrointestinal endoscopy include Cameron’s erosion, fundic varices, peptic ulcers, vasodilatation, and Dieulafoy’s disease. Lesions that are easily missed on colonoscopy include vasodilated malformations and abnormal neoplasms. The etiology of small bowel bleeding varies among patients of different ages, with small bowel tumors, Meckel’s diverticulum, Dieulafoy’s disease, and Crohn’s disease being more common in younger patients, and vascular lesions being more common in older patients (over 40 years old), which can account for about 40% of all etiologies, while other etiologies include small bowel lesions induced by non-steroidal anti-inflammatory drugs (NSAIDs). The introduction and application of capsule endoscopy and double balloon small bowel microscopy have led to a significant breakthrough in the diagnosis and treatment of OGIB in the last 5 years. Due to the new technology, the traditional concept of differentiating upper and lower GI bleeding by the Treitz ligament has been updated to upper, middle and lower GI bleeding. The area above the duodenal papilla and accessible by gastroscopy is called the upper GI tract, from the duodenal papilla to the end of the ileum, accessible by capsule endoscopy as well as double balloon small bowel microscopy is the middle GI tract, and from the colon to the rectum, accessible by colonoscopy is the lower GI tract. Evaluation and diagnosis The degree of GI bleeding and anemia status of the patients were clarified by examination, and OGIB was evaluated in conjunction with the age of the patients. the positive diagnostic rate of small bowel imaging, spiral CT, and radionuclide scan for OGIB was significantly lower than that of capsule endoscopy. For patients with occult gastrointestinal bleeding without anemia, routine upper gastrointestinal endoscopy and colonoscopy are recommended. In patients with occult GI bleeding with anemia, if both upper GI endoscopy and colonoscopy are negative, further capsule endoscopy is recommended, which can help detect small bowel lesions and upper and lower GI lesions that may have been missed by conventional endoscopy. In this group of patients, vasodilatation is the main etiology, accounting for approximately 80% of cases. Based on the results of related studies, it is estimated that less than 10% of patients with small bowel vasodilatation experience gastrointestinal bleeding, and the risk of rebleeding after one episode of gastrointestinal bleeding is 50%. Patients with lesions not detected by capsule endoscopy need to be followed closely, and repeat capsule endoscopy may be considered to improve the positive rate if necessary. During follow-up, approximately half of the patients with positive capsule endoscopy results had rebleeding, whereas only 5% of the patients with negative results had rebleeding. Therefore, patients with OGIB who have negative capsule endoscopy results may defer further invasive testing. 1. Patients with overt GI bleeding with anemia → repeatedly undergo routine endoscopy, with special attention to easily overlooked areas such as the high lesser curvature, below the angular notch, and the posterior wall of the duodenal bulb; 2. For patients with celiac disease, random biopsies of the duodenal mucosa should be routinely taken; 3. Injection of naloxone helps to detect inconspicuous vasodilatation; 4. For patients with suspected pancreaticobiliary lesions duodenal lateral view microscopy. Propulsive enteroscopy should be used in patients who have undergone abdominal aortic aneurysm repair and helps to scrutinize the duodenal C-ring; 5. If all the above tests are negative, capsule endoscopy should be considered. Patients with active gastrointestinal bleeding undergoing capsule endoscopy can clarify the specific site of bleeding. Countermeasures of the lesion: 1. tumor → laparoscopic surgery; 2. proximal small intestine and non-tumor → propulsive enteroscopy with microscopic cautery hemostasis treatment; 3. if the lesion is located in the distal small intestine, double balloon small intestinal microscopy or dissection combined with intraoperative enteroscopy can be considered. 4. Endoscopic surgical treatment is simple and has a good long-term prognosis, and treatment under angiography is limited to cases of acute massive blood loss.